Commonly deployed wireless communications networks support both voice and data services. Typically, mobile handsets or mobile subscribers are connected to a base transceiver station using a radio access network that uses a modulation scheme such as code division multiple access (CDMA) or global system for mobile communications (GSM). The base transceiver stations are connected via fixed links to one or more base station controllers, and the base station controllers are aggregated into switches called mobile switching centers. Mobile switching centers are connected to the public land mobile network/public switched telephone network (PLMN/PSTN), typically through a gateway switch called the gateway mobile switching center (GMSC).
Internet protocol (IP) multimedia subsystem (IMS) is defined by the Third Generation Partnership Project (3GPP) as a mobile network infrastructure that enables the convergence of data, speech, and mobile network technology over an IP-based infrastructure. IMS bridges the gap between the existing traditional telecommunications technology, such as PSTN, and Internet technology, allowing network operators to offer a standardized, reusable platform with new, innovative services by enhancing real time, multimedia mobile services, such as voice services, video telephony, messaging, conferencing, and push services. IMS can be used to provide services for both mobile networks and fixed networks at the same time, providing unique mixtures of services with transparency to the end-user. IMS is one example of a session initiation protocol (SIP)-based network. Another example of a SIP-based network is a next generation network (NGN) network.
IMS supports the establishment of any type of media session (e.g., voice, video, text, etc.) and provides the service creator the ability to combine services in the same session and dynamically modify sessions “on the fly” (e.g., adding a video component to an existing voice session). As a result, new and innovative user-to-user and multi-user services become available, such as enhanced voice services, video telephony, chat, push-to-talk, and multimedia conferencing, all of which are based on the concept of a multimedia session. The underlying IMS infrastructure enables mobile IP communication services via its ability to find a user in the network and then to establish a session with the user. The key IMS components enabling mobility management are the call session control function (CSCF) and home subscriber server (HSS). The CSCF is essentially a proxy, which aids in the setup and management of sessions and forwards messages between IMS networks. The HSS holds all of the key subscriber information and enables users (or servers) to find and communicate with other end users.
A wireline or wireless subscriber may benefit from the call control services provided by both networks. Sometimes the services operated in the different networks provided to a subscriber may overlap. For example, an IMS network may provide the same call control service as a PSTN or 2G wireless network. In some instances, it may be advantageous to offload call control service from one network to another network of a different type. Exemplary network types include 2G wireless networks (e.g., Global System for Mobile Communications (GSM), Interim Standard-41 (IS-41)), Public Switched Telephone Network (PSTN), Next Generation Network (NGN), and IMS networks. For example, the services provided by an IMS network may be cheaper than the PSTN. In this case, it would be advantageous to offload call control services from the PSTN to the IMS network.
Accordingly, there exists a need for methods, systems, and computer program products for offloading call control services from one network to another network of a different type.